lutz: Look Up Time Zones of Point Coordinates

Input latitude and longitude values or an 'sf/sfc' POINT
object and get back the time zone in which they exist. Two methods are implemented.
One is very fast and uses 'Rcpp' in conjunction with data from the 'Javascript' library
(<https://github.com/darkskyapp/tz-lookup/>). This method also works outside of countries'
borders and in international waters, however speed comes at the cost of accuracy - near time
zone borders away from populated centres there is a chance that it will return the incorrect
time zone. The other method is slower but more accurate - it uses the 'sf' package to intersect
points with a detailed map of time zones from here:
<https://github.com/evansiroky/timezone-boundary-builder/>. The package also
contains several utility functions for helping to understand and visualize
time zones, such as listing of world time zones, including information about
daylight savings times and their offsets from UTC. You can also plot a
time zone to visualize the UTC offset over a year and when daylight savings
times are in effect.